Aggregate dryer for asphalt plant

ABSTRACT

Disclosed is a dryer-heater for drying and heating aggregate material prior to its mixing with other ingredients in the production of asphalt paving materials. Drying of the aggregate is accomplished as it moves vertically through an open bin, heat being provided by sinuous passes of tubes carrying hot combustion gases from fuel burners to exhaust stacks; the combustion gases are kept separate from the aggregate so that no dust or fines are discharge from the stack and the sinuous combustion gas tubes are placed so as to efficiently utilize the heat from the burners to dry and elevate the temperature of the aggregate.

United States Patent Davis [54] AGGREGATE DRYER FOR ASPHALT PLANT [72] Inventor: David E. Davis, Indianapolis, Ind.

[73] Assignee: Midwest Steel Fabricators, Inc., In-

dianapolis, Ind.

[22] Filed: Dec. 28, 1970 [21] Appl. No; 101,793

[52] US. Cl ..263/30, 34/ 170 [51] Int. Cl ..F27b 1/08 [58] Field of Search ..263/30, 42 TH; 34/170, 177

[56] References Cited UNITED STATES PATENTS 1,360,336 11/1920 Warrenfeltz ..263/30 591,413 10/1897 Merriman et a1. ..34/l77 [4 1 Nov. 21, 1972 Attorney-Woodard, Weikart, Emhardt & Naughton [5 7 1 ABSTRACT Disclosed is a dryer-heater for drying and heating aggregate material prior to its mixing with other ingredients in the production of asphalt paving materials. Drying of the aggregate is accomplished as it moves vertically through an open bin, heat being provided by sinuous passes of tubes carrying hot combustion gases from fuel burners to exhaust stacks; the combustion gases are kept separate from the aggregate so that no dust or fines are discharge from the stack and the sinuous combustion gas tubes are placed so as to efficiently utilize the heat from the burners to dry and elevate the temperature of the aggregate.

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Manama/MM WW ATTORNEYS AGGREGATE DRYER FOR ASPHALT PLANT BACKGROUND OF THE INVENTION Conventional aggregate dryer units utilize a rotating drum or cylinder, the aggregate being fed into one end and progressing by means of internal flights or blades to the other end where it is discharged. A fuel burner is provided at the discharge end, the flame and hot gases travelling counter to the flow of the aggregates and are drawn out, together with water vapor removed from the aggregates, by an exhaust fan. Since the aggregates are agitated vigorously by the rotation of the drum and the action of the flights, considerable quantities of dust and fine aggregate are entrained in the gas stream and drawn out of the dryer by the exhaust fan. With stricter codes governing the acceptable amount of material discharged from exhaust stacks, the minimizing of this discharge generally requires the installation of relatively high cost precipitators or air cleaners.

The structure of the present invention drys and heats the aggregate efficiently by moving the water vapor resulting from the drying of the aggregate into contact with the wet, cool aggregate entering the drying chamber, causing the water vapor to condense and give up its heat of vaporization to the incoming aggregate material. This is accomplished by introducing the aggregate to be dried and heated at the top of a vertical tank or column having sinuous tubes passing through the tank at its lower levels, the tubes carrying hot combustion gases which are discharged into exhaust stacks without agitation of the aggregates, and without these gases making direct contact with the aggregates, the heat conducted and radiated from the tubes to the aggregate serving to dry it and raise it to the proper temperature prior to mixing with the other asphalt ingredients. An apertured plate at the base of the column, below the burner tube passes, is reciprocated to alternately mask and unmask the plate apertures, thereby permitting the dried and heated aggregate to exit from the column through the plate apertures at a generally uniform rate over the cross-section of the column base so that the aggregate moves uniformly through the vertical column in the drying and heating operation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of an apparatus embodying the present invention.

FIG. 2 is an end view of the apparatus shown in FIG 1.

FIG. 3 is a fragmentary end view, with obscuring parts removed, of the lower portion of the apparatus shown in FIG. 1.

FIG. 4 is a side view, with obscuring portions broken away, of the lower portion of the apparatus shown in FIG. 1.

FIG. 5 is a sectional view taken generally along the line 5-5 ofFIG. 4.

FIG. 6 is a fragmentary top plan view of a portion of the apparatus shown in FIG. 5.

FIG. 7 is an enlarged view illustrating the connection of the actuating hydraulic cylinder with the apertured plate shown in FIG. 4.

FIG. 8 is a fragmentary, top plan view of a portion of the apparatus shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT The apparatus for heating and drying aggregate material of the present invention includes a vertically disposed rectangular column 10 adapted to receive raw (unheated, damp) aggregate at its upper end 11. The apparatus ejects dried and heated aggregate at its lower end through the exit aperture 12 as will subsequently be explained.

Intermediate the upper and lower ends of the hollow rectangular column or tank 10 a series of heat exchange tubes extend across the column. The upper row of tubes 13 include sinuous, horizontal tube passes 14 (FIG. 1) which extend across the column and terminate at 16 where the continuous passage formed by the tube passes 14 communicates with the exhaust stack 17. The other end of the continuous passage formed by the tube row 13 communicates with a fuel burner indicated generally at 18 which may be of either an oil burning or gas burning type, the tube passes 14 serving to convey the hot combustion gases from the burner 18 to the discharge stack 17. Similarly, the next lower horizontal row 19 of burner tubes is formed by the sinuous passes of the tubes identified at 21, these burner tube passes forming a continuous combustion gas conducting passage from the fuel burner to the discharge stack 23. The next lower row 24 of horizontal tube passes 26 serve to conduct combustion gases from the burner 27 to the exhaust stack 17, the junction between the burner tubes 26 and the exhaust stack 17 being indicated at 28.

The two lower rows of heat exchange tubes have a somewhat different configuration in that each of the two burners 30 and 32 supply combustion gases to heat exchange tubes lying at vertically spaced levels in the column 10. Thus, the burner 30 supplies combustion gases to the adjacent, overlying heat exchange tubes 31 which form but one-half of the complete horizontal row of tubes, the tubes 31 communicating with the adjacent underlying tubes 32 which form onehalf of the lowest horizontal row of tubes. The tubes 31 and the communicating parallel tubes 32 form a continuous passage for combustion gases from the burner 30 to the discharge stack 23. Similarly, the horizontal tube passes 33, forming one-half of the horizontal row of tubes, which includes the tube passes 31, communicate with the horizontal tube passes 34 which form a portion of the lowest horizontal row of tubes, which includes the tubes 32, and these interconnected tubes 33 and 34 form a continuous passage for hot combustion gases from the burner 32 to the exhaust stack 36, it being understood that the exhaust stacks 17, 23 and 36 all extend upwardly, exteriorly of the tank 10 on the side of the tank opposite from that on which the burners are mounted. A centrifugal blower 37 serves as an air supply for the burners through the plenum duct 38 which communicates with the air intake of the burners 18, 22, 27, 30 and 32. The column 10 and attached equipment is supported on vertical legs 41 and, it will be understood, that heated and dried aggregate exiting through the aperture 12 is deposited on a conveyor of any suitable type (not shown) and the aggregate is thereby transported to the proper point in the asphalt plant where it is mixed with other ingredients in the asphalt manufacturing process.

Drainage compartments 42 are mounted on the column 10, just above the upper row 13 of heat exchange tubes and the interior of the compartments 42 communicate with the interior of the column. Each of the compartments 42 is provided with an inclined weir 43 leading to a discharge tube 44 which extends to a suitable drain or water storage point (not shown). Water drains from the column into the compartments 42 and into the condensed water drain tubes 44 as will subsequently be described, the weirs or baffles 43 serving to prevent aggregate material from washing into the drain tubes 44.

A hydraulic cylinder, indicated generally at 46 is trunnion mounted at 47 on the bracket 48 which extends from the lower portion of the tank structure, this hydraulic cylinder serving as the power means for reciprocating an apertured plate in a limited horizontal motion as will subsequently be described. It will be understood that other forms of drive for the plate could be utilized.

The structure for releasing aggregate material uniformly across the base of the column will now be described and includes the generally rectangular housing 51 which, as may best be seen in FIG. 2, is attached to and depends from the base of the column 10 adjacent the support legs 41. As may best be seen in FIG. 4, the housing 51 supports for rotation therein shafts 52 and 53 which carry spaced sprockets 52a and 530, the shaft 52 being driven by an exterior motor (not shown) and supported by bearings 54. Extending around the sprockets 52a and 53, at each side of the housing 51 are flexible chains indicated schematically at 56 in FIG. 4, spaced links 56a of the chain 56 carry transverse angle iron members forming transverse slats or scrapers 57 which, as the lower pass of the chain moves from right to left in FIG. 4, engage and impel aggregate material which has dropped to the base 51a of the housing 51 toward the aperture 12 in the housing, the assembly thus forming a drag-conveyor which moves material resting on the base 51a of the housing out through the aperture 12. The means for providing a uniform flow of aggregate material from the base of the column 10 into the housing 51 includes a grid formed by an upper group of spaced parallel members 61 and a lower group of similar members 62, the two series of members being transverse to each other and formed by angle irons oriented so that the longitudinally ridged portions 62a and 61a extend upwardly toward the heat exchange tubes. As may best be seen in FIG. 6, the generally square configuration spaces 63 permit access to an underlying apertured plate 64 (FIG. 4) which carries a series of round apertures 66 therein, the apertures as shown in FIGS. 4 and 6 generally registering with the grid openings formed between the members 61 and 62. As may best be seen in FIGS. 3 and 5, the plate 64 is supported on depending V-shaped runners 67, the runners being attached to brackets 68 which are, in turn, rigidly attached to the underface of the plate 64. The runners 67 are accommodated on and slide along the mating track members 69 which are rigidly secured to structural members 71 which extend across the structural frame members 72 framing the lower portion of the column 10. The track members 69 and runners 67 are spaced along the width of the column framing members and the adjacent faces of the members 69 and 67 may be provided with a suitable anti-friction facing.

The plate 64 is thus capable of being moved a limited amount in the direction of extension of the tracks 69 so as to alternately mask and unmask the plate apertures 66 as they are alternately placed in register with the spaces 63 between the members 61 and 62. The means for providing this reciprocating, limited horizontal motion to the plate 64 is, as previously mentioned, the hydraulic cylinder 46. As may best be seen in FIGS. 7 & 8, the thrust member 76 operated by the hydraulic cylinder has a threaded connection with the yoke 77 and the yoke has a pivotal connection with the member 78 which is rigidly attached to a bracket 79 rigidly secured to the plate 64. Thus, as the thrust pin 76 is reciprocated horizontally (as viewed in FIG. 7), the plate 64 will be given a corresponding reciprocating, horizontal motion.

In operation, the raw aggregate material, damp and at a temperature lower than that proper for its entry into the asphalt making process, moves downwardly through the column 10 and is removed uniformly across the cross-section of the column by means of the grid and apertured plate 64. The first three rows of heat exchange tubes 13, 19 and 24 serve primarily, a drying function, the operating temperature of the three burners 18, 27 and 22 being set so that the water in the ag gregate is vaporized without the temperature of the aggregate being substantially raised. For example, the dry aggregate moving to the area below the row of heat exchange tubes 24 might be 250F. The lower two rows of burner tubes and the heat exchange tubes and the burners 30 and 32 which supply hot combustion gases to them primarily serve to raise the temperature of the now dry aggregate to that best suited for the asphalt making process. The lower two burners 30 and 32 are preferably controlled separately from the burners providing heat for the upper three. rows of heat exchange tubes, the control point of the lower burners 31 and 32 establishing the temperature of the dried aggregate material. As the water in the aggregate is vaporized by the heat radiated and conducted from the upper three rows of heat exchange tubes, the water vapor rises and upon meeting the entering unheated aggregate material at the top of the column 10, the vapor is re-condensed and forms, in effect, a layer of water in the upper marginal area of the column and this water is drained away through the drainage compartments 42.

It will be understood that the amplitude and frequency of the movements of the apertured plate 64 can be adjusted by any suitable means such as by altering the control valving to the hydraulic cylinder 46 or by adjusting or altering the linkage between the hydraulic cylinder and the apertured plate.

I claim:

1. An apparatus for heating and drying aggregate material, said apparatus comprising a vertically disposed hollow column adapted to receive unheated damp aggregate at its upper end and to eject dried and heated aggregate at its lower end, the base of said column being spanned by a grid formed of a first series of uniformly spaced and parallel longitudinally ridged members and a second series of uniformly spaced and parallel ridged members overlying the first series and extending transversely thereto with the peaks of the longitudinal ridges of said members directed upwardly and the interstices between saidv members forming the open spaces of said grid, an apertured plate closely underlying the grid formed by said spaced members, means for horizontally reciprocating said plate relative to said grid to thereby intermittantly mask and unmask portions of said plate apertures, a series of heat exchange tubes extending across said column intermediate its ends, said series of heat exchange tubes having a sinuous configuration with the tubes being staggered vertically with relation to each other to facilitate heat transfer between said tubes and the aggregate material moving past them, and burner means discharging combustion gases into said tubes, whereby heat transferred from said tubes to the aggregate vaporizes the moisture in the aggregate and the vapor rising in said column is again condensed as it encounters the unheated aggregate at the area in said column adjacent to and above the uppermost of said heat exchange tubes.

2. An apparatus as claimed in claim 1 having conveyor means disposed beneath said grid and apertured plate for removing aggregate material passing through said plate apertures.

3. An apparatus for heating and drying aggregate material, said apparatus comprising a vertically disposed hollow column adapted to receive unheated damp aggregate at its upper end and to eject dried and heated aggregate at its lower end, a series of heat exchange tubes extending across said column intermediate its ends and spaced below the aggregate material level in said column, said series of heat exchange tubes having a sinuous configuration with the tubes being staggered vertically with relation to each other to facilitate heat transfer between said tubes and the aggregate material moving past them, burner means discharging combustion gases into said tubes, whereby heat transferred from said tubes to the aggregate vaporizes the moisture in the aggregate and the vapor rising in said column is again condensed as it encounters the unheated aggregate at a recondensating level in said column located intermediately between the aggregate material level in the column and the uppermost of said heat exchange tubes, and condensate draining means extending from said column adjacent said level of recondensation. 

1. An apparatus for heating and drying aggregate material, said apparatus comprising a vertically disposed hollow column adapted to receive unheated damp aggregate at its upper end and to eject dried and heated aggregate at its lower end, the base of said column being spanned by a grid formed of a first series of uniformly spaced and parallel longitudinally ridged members and a second series of uniformly spaced and parallel ridged members overlying the first series and extending transversely thereto with the peaks of the longitudinal ridges of said members directed upwardly and the interstices between said members forming the open spaces of said grid, an apertured plate closely underlying the grid formed by said spaced members, means for horizontally reciprocating said plate relative to said grid to thereby intermittantly mask and unmask portions of said plate apertures, a series of heat exchange tubes extending across said column intermediate its ends, said series of heat exchange tubes having a sinuous configuration with the tubes being staggered vertically with relation to each other to facilitate heat transfer between said tubes and the aggregate material moving past them, and burner means discharging combustion gases into said tubes, whereby heat transferred from said tubes to the aggregate vaporizes the moisture in the aggregate and the vapor rising in said column is again condensed as it encounters the unheated aggregate at the area in said column adjacent to and above the uppermost of said heat exchange tubes.
 1. An apparatus for heating and drying aggregate material, said apparatus comprising a vertically disposed hollow column adapted to receive unheated damp aggregate at its upper end and to eject dried and heated aggregate at its lower end, the base of said column being spanned by a grid formed of a first series of uniformly spaced and parallel longitudinally ridged members and a second series of uniformly spaced and parallel ridged members overlying the first series and extending transversely thereto with the peaks of the longitudinal ridges of said members directed upwardly and the interstices between said members forming the open spaces of said grid, an apertured plate closely underlying the grid formed by said spaced members, means for horizontally reciprocating said plate relative to said grid to thereby intermittantly mask and unmask portions of said plate apertures, a series of heat exchange tubes extending across said column intermediate its ends, said series of heat exchange tubes having a sinuous configuration with the tubes being staggered vertically with relation to each other to facilitate heat transfer between said tubes and the aggregate material moving past them, and burner means discharging combustion gases into said tubes, whereby heat transferred from said tubes to the aggregate vaporizes the moisture in the aggregate and the vapor rising in said column is again condensed as it encounters the unheated aggregate at the area in said column adjacent to and above the uppermost of said heat exchange tubes.
 2. An apparatus as claimed in claim 1 having conveyor means disposed beneath said grid and apertured plate for removing aggregate material passing through said plate apertures. 